For the transmission of video contents on the Internet for services such as Internet TV or video on demand, in the context of the known DVB system (Digital Video Broadcast), a specification was created which defines a transmission protocol according to which such digital video contents can be transmitted via the Internet. The specification is known under the designation DVB-IPI (Digital Video Broadcast Internet Protocol Infrastructure). This specification describes, inter alia, the coding of information for the description and selection of audio/video data streams (also called AV streams) in the form of XML documents. In the specification this information is also designated as “Service Discovery & Selection” information (corresponding to SD&S). The exact designation of the DVB-IPI specification reads as follows: Digital Video Broadcasting (DVB); “Transport of DVB Services over IP”: DVB Document A086, July 2004.
The SD&S data contain information about the service providers themselves and about their various service offerings (Live Broadcast, Content on Demand, AV Streaming with Trick Modes, etc.). In this case, the data are structured as follows: the type of SD&S data is indicated by the so-called payload ID. The data belonging to a payload ID of a service provider are designated as the so-called SD&S data record. An SD&S data record is typically subdivided into a plurality of independent segments, so-called SD&S segments, in order to limit the effects of possible changes to as few segments as possible. However, a data record may also comprise a single segment. Each SD&S segment of a service provider is identified by the combination of payload ID and segment ID. In order to be able to signal changes of a segment, each segment additionally has a version number, the so-called segment version number. If the data of a segment change, the version number of the segment has to be incremented in order to indicate the change and to enable the retrieval of this specific version. In the DVB-IPI specification, two different transmission modes are described for the transmission of the SD&S data. In addition to the retrieval of SD&S data by HTTP (Hyper Text Transfer Protocol), which is also referred to as the so-called “Pull Mode”, DVB-IPI specifies the transmission protocol DVB-STP, by which the data of an SD&S server of a service provider are periodically transmitted by UDP (Multicast) to all interested receivers. This mode is designated as the “Push Mode”. UDP corresponds to the known “User Datagram Protocol” from Internet technology. The invention that is to be described is principally used in the “Push Mode”. In this mode, the SD&S segments are optionally fragmented further into so-called SD&S sections, and provided with a DVB-STP header. Such a section is periodically sent as a UDP packet by multicast.
On the basis of the service provider ID, which is derived implicitly from the IP multicast address or is explicitly specified, the payload ID, the segment ID and the segment version number, the receiver combines the segments again from the individual sections and processes the SD&S data contained in order to be able e.g. to display an electronic program guide. The receiver identifies changes of a segment from the changed segment version number, and it can thereupon replace the old data with the new data. However, the decision as to which data are the old data and which are the new, on account of the unsecured transmission by UDP, is not as trivial as it might at first appear.